No, their parents married literally a few months ago. They live in a huge castle and never see each other because they don’t like each other at first—neither are willing to even acknowledge the marriage essentially—they do not see each other as family at all. Not even as acquaintances as strangers—they won’t talk to each other even as strangers. They didn’t know each other at all beforehand.
I will say that irl I wouldn’t approve. I don’t think it necessarily would be the end of the world but I would advise against it. Irl they couldn’t be living in the same household that’s for sure—like they couldn’t be dating at all. Only if they were adults living on their own and moved out of their parents home.
I will say that I’m not a completionist—there’s lots of Otome games where I literally only play one route and don’t play any of the others if I don’t like them. Rod’s route is my favorite in this game because of his personality. Karma was my second favorite. I didn’t like Fritz or Rumpel—this was my first Otome game I ever played so I did finish these routes, but I would have skipped them if I was playing the game for the first time today. Waltz was just okay.